We tend to pile on too much with the reasoning: saying "no" means letting someone down. You want to seem proficient so you stay on even when you need off time. No good if you are human. The honesty of it is-we get tired, we have bad days, we come to our wits end, and you know what? This is perfectly ok to do. It does not give us license to unload issues onto an unsuspecting souls we happen to cross paths with, but it does mean you recognize that you are not infallible.
Smartphones wise up note taking with voice messaging, all you have to do it follow up. One way to prevent overbooking yourself is by taking time to process what is on your calendar. The voice recording app doesn't always get it right so I have a hardcover day planner, that's right I said it. No shame in it either. I schedule 15 minutes to review appointments, meetings, networking. Before you know it I have solidly locked plans and no worries. I have learned not to overextend myself which means understanding my own limitations and boundaries.
Sticky notes prove invaluable but you can quickly become mummified if all you do is take notes. Try instead to organize your thoughts by the hour, making callbacks sooner than later keeps you accountable. Note threshold: 10 per hour to make good on promises of a return call. Take breaks instead of thinking that you have to tough it out and make every call back in 5 minutes, which isn't fair to you or your clients and potentials.
If all else fails, step away from the desk for a moment. Put the phone down and just breathe. Whatever it is you need to accomplish is not that serious so as to make you miss the point of the day-enjoying life. If you can't go sailing, this just might be the best throwback mood improver of the week. https://www.youtube.com/watch?v=7khQNR7s1Ho
Until next time~